A2337 820-02016 power won’t turn on

[Araibu]

Hi. This is my first post. I am studying troubleshooting for motherboard. I would like to learn something from all of you. Thank you.

I have an 820-02016 that won't power on. The USB-C voltage is around 5V and it's consuming almost 0A of current. There's a clicking sound coming from the motherboard.

PPBUS_ANON → 12.33V
(FP800-1)

PP3V8_AON_VDDMAIN → The voltage is unstable(approximately 5 to 10V)
(C5887-1)

I’m not sure what to do for the next troubleshooting step, any suggestions are welcome. Thank you.

 

[2informaticos]

First of all, welcome to the forum!

Any fault history available?

"PP3V8_AON_VDDMAIN → The voltage is unstable(approximately 5 to 10V)"
That's strange and dangerous.
Check diode mode to ground there.

PPBUS_AON is really stable?

 

[Araibu]

First of all, thank you for the warm welcome to the forum! I appreciate your response and look forward to engaging in meaningful discussions here.

Any fault history available?

→No, there is no fault history available. However, the device suddenly stopped powering on.

Check diode mode to ground there.

→When I checked at C5887-1, the voltage keeps rising. I apologize if I made a mistake in the checking method.

PPBUS_AON is really stable?

→PPBUS_AON is stable. I also checked other components, and they were the same.

C5962-1
C5963-1
C5964-1
→All were at 12.33V

 

[2informaticos]

"When I checked at C5887-1, the voltage keeps rising"
Did you disconnect battery and charger?

HOW TO collection

I hope this "How to" collection will help our members. I will possibly modify this post in time, if updates available. Trigger SMC_ONOFF_L (PMU_ONOFF_L): It reffers to simulate power button function, when the keyboard is not connected. We need to do this when we work with the board...

boards.rossmanngroup.com

 

[Araibu]

Thank you for your reply.

Did you disconnect battery and charger?

→Yes, I have disconnected both the battery and the charger.

HOW TO collection
Test in diode mode:
Connect positive probe of the multimeter (red) to ground and touch the test point with black probe.
Sometime (rarely) we need to test in reverse direction.
→I checked it the way you suggested and it was 0.157V. I had the red and black reversed. I apologize for the confusion.

 

[2informaticos]

That value looks good.

The clicking sound may be caused by a short on a secondary power supply.
You should check them all and compare with good board (diode mode), or reference tables.

OpenBoardData Project

Start with 3V3/5V_S2 lines and backlight.

 

[Araibu]

Thank you for your advice.
I will check all of them and compare with a good board (in diode mode) or reference tables. I will start with the 3V3/5V_S2 lines and backlight as you suggested. I will get back to you with the results.

 

[2informaticos]

I was talking about secondary power rails.
Doesn't mean to check same line on various points; which are tied together. (eventually through 0 ohm resistors).

You've posted even GND to GND measurment (GND_BKLT_SGND).
Try to put some logic on your job!
Posting in such manner, doesn't help.

I was expecting readings from pages 36 & 40.
Also all coils around U8100 and U7700; be aware, some of them are tied together.

 

[Araibu]

Thank you for your feedback.

I realize now that my approach may have lacked the necessary logic and I will strive to improve this in the future. I understand that my previous posts may not have been helpful and I appreciate your patience.

Regarding the readings from pages 36 & 40, I believe you might be referring to the Rossmann Repair Training Guide. Could you please confirm this? If so, I will make sure to focus on these pages for the readings.

I will also pay close attention to all coils around U8100 and U7700, keeping in mind that some of them are tied together. I appreciate your guidance and look forward to your confirmation on the reference material.

 

[2informaticos]

I meant pages 36 & 40 from schematic...

 

[Araibu]

Thank you for clarifying that the pages 36 & 40 refer to the schematic. I appreciate your guidance and will make sure to focus on these pages in the schematic for my readings.

 

[2informaticos]

Pay atention to output rails in the mentioned pages.

 

[Araibu]

The clicking sound may be caused by a short on a secondary power supply.
You should check them all and compare with good board (diode mode), or reference tables.
OpenBoardData Project Start with 3V3/5V_S2 lines and backlight.

I appreciate your guidance so far.

However, I’m still feeling a bit uncertain about whether I’m following the correct procedure. Could you please provide me with more specific steps or methods to check the secondary power supply?

I apologize for any inconvenience and truly value your expertise and assistance in this matter.

 

[2informaticos]

If we talk about page 36, you have 2 outputs (VOUT), for UC100/20.

On page 40, you have 1 output (VOUT) for UC810 and another (S) for UC820; D is its input.
UC840/50 have each 2 outputs; OUT and FLT*.

For backlight, good enough to check one of CP86x capacitors.

About common coils.
Once you've checked at L8270 (for example), no reason to check L8271 too.

 

[Araibu]

I greatly appreciate your reply. Your assistance has been extremely valuable.

If we talk about page 36, you have 2 outputs (VOUT), for UC100/20.

→With the charger connected, both CC101-1 and CC121-1 measured -00.1mV.

On page 40, you have 1 output (VOUT) for UC810 and another (S) for UC820; D is its input.
UC840/50 have each 2 outputs; OUT and FLT*.

→Even with the charger connected,
the voltage was nearly 0V.
UC810-3 00.4mV
UC820-3 00.5mV
UC820-5 00.1mV
UC840-5 00.0mV
UC840-6 -00.1mV
RC851-2 -00.1mV
LT400-1 00.0mV

For backlight, good enough to check one of CP86x capacitors.

→With the charger connected, CP860-1 measured 00.2mV. It seems like a short circuit was not occurring.

I hope my understanding is correct and the information I provide will be useful. However, I’m a bit uncertain about whether my information will be helpful to you. Could you please confirm if I’m on the right track? If there are any mistakes in my verification method, I apologize. Your guidance is greatly appreciated.

 

[2informaticos]

Yeah, we already know that you don't have mentioned voltages.
For this reason, I was expecting diode mode readings on these outputs!

Don't forget to disconnect charger and battery...

 

[Araibu]

I apologize for any inconvenience caused. The diode mode readings for these outputs are as follows.

CC101-1 0.484V
CC121-1 0.410V
UC810-3 0.485V
UC820-3 0.308V
UC820-5 0.381V
UC840-5 0.189V
UC840-6 0.635V
UC850-5 0.189V
RC851-2 0.472V
CP860-1 1.085V

I compared it with the reference table and there was no significant difference. Could you tell me what I should check next?

 

[2informaticos]

You forgot the coils around U7700 and U8100...

 

[Araibu]

About common coils.
Once you've checked at L8270 (for example), no reason to check L8271 too.

You forgot the coils around U7700 and U8100...

Thank you for pointing that out.

️U8800
L8100→0.017V
L8110→0.020V
L8120→0.019V
L8230→0.305V
L8270→0.177V
L8280→0.104V
L8290→0.224V
L82B0→0.058V
L84E0→0.277V

️U7700
L7740→0.036V
L7750→0.225V
L7760→0.348V
L77A0→0.137V
L77C0→0.307V
L77D0→0.250V
L7800→0.155V

I’ve compared the results with the reference table and found several values that are lower. Could you please advise on the next steps?
I hope my understanding is correct and the information I provide will be useful.

 

[2informaticos]

Please, STOP writing "V" after diode mode readings; avoid confusion with voltage checking.
The voltage you get in diode mode, is in fact generated by your multimeter, which injects constant current on the board.

Looks to have very low values around U8100.
Just for test, remove L8120/1 and R810C; check where the low value remains.